Gyakuten Kenji, literally meaning Turnabout Prosecutor, is a spin-off game which features Miles Edgeworth as the main character, alongside Dick Gumshoe. After a short period of speculation over a trademark filed by Capcom, it was finally revealed the English localisation of the name was indeed Ace Attorney Investigations. Prior to this, some fans had referred to the game as Miles Edgeworth: Perfect Prosecutor.

In Japan, as well as the standard edition, is a limited edition set. This includes, along with the game of course, a mini-album, a pamphlet for the Spring orchestra event, some artwork cards, a card case and a DVD of trailers.

Also, to celebrate the release of the game in Japan, a special "Premium Edition" bundle of the game and a white Nintendo DSi console is going to be released featuring a logo of the blue badger on it.

There is also a Gyakuten Kenji manga which began publishing shortly before the game was released in Japan.

The game itself will differ slightly in gameplay to the previous incarnations in the series. The Investigation phases still exist, but will be presented in a 3rd person view, and Edgeworth can consult his current partner on his findings. As there will be, or so it seems, no court phases, there is instead Confrontation phases which act in a similar way to the court phases in the previous games.

Logic and Deduce options are new to the series. The first uses Miles' superior intellect to piece together fragments of his thoughts, forming a logical conclusion concerning the case at hand. When exploring an environment and viewing a specific scene or object up close, the player can now use Deduce to find new clues or evidence. Edgeworth's catchphrase shout is Eureka when evidence is presented correctly, similar to Phoenix Wright's objection.

There is also the crime re-enactment stages with the use of Kay's "little thief" device, where Edgeworth can go through the crime scene to try and see things from that perspective.

This is the 5th game in the series, although chronologically it would be the 4th, set roughly one month after the events of Phoenix Wright: Trials and Tribulations. There is also one flashback case set 7 years before the start of the game.

A flashback case where Edgeworth is still under the wing of Manfred Von Karma. This is due to be Edgeworth's first case, however it is cancelled after both the defendant and the previous prosecutor involved are killed.